遺傳的畸形蚕の發生と卵細胞質(豫報)

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It was found during the summer of 1946, that silkworm eggs treated with a dilute solution of hot hydrochloric acid (so-called the artificial hatching method) produced some mutants in the bivoltine race of J. No. 105. This mutant is characterized by a disorder of the seventh to ninth dorsal abdominal segment (see, fig. 1, a, b). The appearance of this mutation is not always constant, it is being controlled by some external factors. There is generally a higher frequency of occurrence, when the eggs are treated about 25 hours after being laid. When treated later than 45 hours, the mutation rate is lower or negative. The latter state is also found in worms raised from the hibernating eggs without any stimulation. According to further morphological observations, it is found that stages to 35 hours old (pyriform embryos) from the time of fertilization are most susceptible to such a stimulus, the highest frequency beiug found in 25 hours old (see, fig 2, c). The results of the crosses between the normal strain and the normal are as follows: In the F_1 generation, when a female of the abnormal strain is crossed with a male of the normal, abnormals appear at the rate of 5.3%, though none are found in the reciprocal case. However, the F_2 of the reciprocal cross produces abnormals at a lower frequency. Such no appearance of abnormals in the reciprocal cross is striking evidence that the development of abnormalities must be due to deformation of ooplasm. On the other hand, a lesser frequency of the abnormality in the F_2 generation is enough to demonstrate that a mutant gene in this connection must play a part in the defect of the ooplasm. The critical period of predetermination in such abnormalities initiated by the deformation of ooplasm, was thought to be limited by the pyriform stage inclusive of about 35 hours old. Thereafter, the embryonic development seemed to be controlled by a gene regarding the normal formation of ooplasm. The embryonic development of the animal egg is divided into two types, regulative and mosaic. Most insect eggs belong to the latter type. The general embryology of our eggs, however, was not according to such differentiation, as clearcut as we expected. It is thought to be limited by a particular embryonic stage, never extending further to the later stages. That is a problem to be discussed. At least, adequate evidence regarding it, is not yet known in the Lepidoptera, though is indicated to some extent, by Seidel ('29, '38) on Platycnemis in the Odonata. From our scattered investigations on the development of abnormalities in the above case, it will be more profitable to discuss the following point: Predetermination of specific characters based on the cytoplasm of the egg seems to be limited by the pyriform stage, till about 35 hours after being laid. The number of cells of the serosa, though varying more or less according to the race of silkworm, is found to be about 800 and probably less in the pyriform embryos of 35 hours age. The number of cell divisions from fertilization to the pyriform stages is thought to be within the limit of 2^<10-11> in the silkworm eggs. In general, the occurrence of such hereditary abnormalities may be always explained by the theories of modifying genes. The present case can be explained by the environmental factors, such as the plasmagenes being the cytoplasmic activatory as proposed by Sonneborn ('49). This possibility must not be neglected, and such a phenomenon can also explained by replacing modifiers by the theories of plasmagenes. In order to solve the question, further investigations on the embryological as well as the cytological aspects must be carried out in the future.
社団法人日本動物学会の論文
1950-12-15

遺傳的畸形蚕の發生と卵細胞質(豫報)

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